Deathsinger is incredibly simple if you practice it enough. To begin, start with the left side. If you have Gally, hide behind a pillar and wait for the boomer knight to walk out. Run in, shoot 2 Gally shots at the wizard and finish her off with primary. Jump on top of a doorway, and kill shrieker. Proceed to the other side and continue in the same manner. After the right shrieker is dead, clear out all the knights and acolytes. Jump on a doorway and snipe the deathsinger until she begins singing. If she is visable after she begins singing, simply snipe her down. If she hides behind the crystal, jump to the opposite doorway in which you came in. If you cleared all the enemies, you will not be shot. Kill deathsinger and carefully exit the crystal room. Congrats, you just solo'd deathsinger.